Ok, i have an '89 Chevy Caprice w/ 65k. Its a 305 V8 motor and it has bad seals. It burns oil on startup and when cold. Anyway, i've been using valvoline 10-W30 all year round since i live in chicago and it usually gets pretty warm. I have the following oil choices: Castrol GTX Valvoline Chevron Supreme Pennzoil Which one is considered the best oil with regards to lasting long and having good flash points etc. And why the heck is chevron so cheap? its about 1.14 a quart and the others are usually at least .50 cents more. What do you guys think?